Circuit-arrangement for operating a loudspeaker installation



Sept. 3, 1957 H FlNLAY 2,805,285

CIRCUIT-ARRANGEMENT FOR OPERATING A LOUDSPEAKER INSTALLATION Filed Aug. 13, 1953' AMPLIFIER INYENTOR v HANS mm. A' y.

United States Patent @r ClRCUIT-GEh/IENT FOR OPERATING A LQUDPEAKERTNSTALLATION Hans Finlay, Bielefeld, Germany, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application August 13, 1953', Serial No. 373,983

Claims priority, application Germany August 21, 1952 5' Claims. (Cl. 179-2) The present invention relates to a selective switching circuit arrangement for loudspeakers. More particularly, the invention relates to a circuit arrangement for operating a loudspeaker installation with the use of a line initially present for other purposes, preferably for local announcing or municipal radio broadcasting.

When using such local or municipal broadcasting apparatus, lines of considerable length are sometimes laid out for the loudspeakers to be connected. In many places the same location may be chosen for the loudspeakers as that selected for the installation of street lighting equipment. The use of power lines initially present for street lighting, consequently avoids the necessity for a separate loudspeaker network for energizing the loudspeakers.

When the power in the power lines is switched ofi, the street lighting network is available for other than street lighting.

The present invention has the feature that the line comprises a relay for each loudspeaker or group of loud speakers. Each relay is energized from a central station by a direct voltage impressed on the line and connects the loudspeaker or lighting means to the line, as required, the voltage required each time being simultaneously applied to the line by means of a switch at the central station. The advantage of the circuit-arrangement according to the invention is that it is much simpler and consequently less liable to disturbances than prior systems. Moreover, it is more economical to install than prior systems.

In a circuit-arrangement according to the invention, the switch at the central station advantageously does not connect the audio-frequency amplifier simultaneously to its supply until it applies the low frequency voltage to the line. This insures that the amplifying installation can only be operative if the loudspeaker installation is available for radiating the amplified voice voltages and is connected to the amplifier.

Alternately, a relay or the like may be substituted for the hand-operated switch at the central station. Such a relay may be operated via an associated connecting lead from an arbitrary location. Such a circuit-arrangement may be advantageous, since the location of the microphone for intelligence to be transmitted via'the loudspeakers is often not in the immediate proximity of the central station. Instead of using a relay, a different switching device, for example a step switch or other automatic device, may be used in accordance with the conditions imposed.

The line relays changing over to the lighting means may advantageously be energized by a direct current superposed on the audio-frequency voltage and may be maintained in this state during the transmission of intelligence signals over the line. Thus, it is ensured that, in the event of failure of the relay control, the lighting means concerned is at any rate connected to the line. The initial purpose of the network is therefore not adversely afiected by the additional device.

Another advantage of the invention is due to the fact .that a direct current impulse serves to operate the line relays, the relays being of the type having two stable rest Patented Sept. 3, 1957 positions, for example in themanner of polarised relays. Thus, it is not necessary to constantly maintain a direct current during the transmission of intelligence signals over the line in order to control the relays. Notably in large installations, a considerable total direct current occurs as aresult of the large number of relays to be controlled. This should be avoided, not only in view of the additional consumption of energy, but also on account of the fact that otherwise additional technical means are required for decoupling between the direct current and the low frequency transmitters and so on.

For operating the. line relays a key or the like may be provided at the central station, said key being operated to send a direct current impulse through the line in order to change over all the relays from one position to the other.

The installation and its control are simplified by causing the switch at the central, station to send in a constrained manner a direct current impulse through the line, after having switched 05 one alternating voltage and prior to connecting the other alternating voltage to the line. In the simplest case, such a switch may, for example comprise a unipolar three-way type, the middle contact being intended for the supply of direct current, so that on changing over it is urged from one position into the other in a constrained manner.

In order that the invention may be readily carried into efifect. it will now be described with reference to the accompanying drawing. in which:

Fig. 1 is a schematic diagram of an embodiment of the circuit arrangement of the present invention; and

Fig. 2 is a. schematic diagram of another embodiment of the circuitarrangement of the present invention.

In Fig. 1, direct current is continuously transmitted during the transmission of intelligence signals. The reference numeral 1 designates the power line, to which the street lighting means are connected. The central station comprises an amplifier. 2, at the output of whichthe audiofrequency intelligence voltages are available, a direct current supply source 3 and a switch 4. In one position of the switch 4, the line 1 is connected to the power supply source. In the other position of the switch 4, the series combination of the amplifier 2 and the direct current supply 3 is connected to the line 1.

A loudspeaker or a loudspeaker device 6 is assumed to be situated in the immediate proximity of each street lighting means 5. A connecting device 7 comprises a relay 8 for switching in the loudspeaker 6 or the lighting means 5.

If the switch 4 is connected to the power supply source, the lighting means 5 is connected to the line 1 via a relay armature 8' and a Winding portion of the energizing of the relay 8. The relay 8 does not respond to the supply current of the lighting means 5. The loudspeaker 6 is shunted by the armature 8' to avoid hum. A fuse 9 protects the loudspeaker 6 in the event of defective operation of the relay contact 8.

If the switch 4 is operated at the central station, not only the output voltage of the amplifier 2, but also the direct voltage of the supply source 3 are applied to the line 1. A direct current passes through the energizing winding of the relay 8, the relay armature 8 and the lighting means 5, and energizes the relay 8. Upon energization, the relay 8 removes the shunt of the loudspeaker 6 and short-circuits the lighting means 5. The direct current then flows through the energizing winding of the relay 3, the loudspeaker 6 and the relay armature 8', said relay remaining in this condition, as the case may be upon a direct current decrease. The intelligence currents of the amplifier 2 are now allowed to pass to the loudspeaker or loudspeaker device 6. The relay 8 is shunted by a capacitor 10 which serves to pass the alternating currents passed I 7 3 by the relay winding which, due to its self-induction would otherwise constitute a considerable impedance with respect to the alternating current.

In Fig. 2, the change over is efiected by direct current impulses. In the circuit-arrangement shown in Fig. 2 the same reference numerals are used for corresponding components as in Fig. 1. The circuit-arrangement shown in Fig. 2 comprises a relay 8 whose armature 8 has two stable positions of equilibrium, a current impulse in the relay energizing winding solely causing the armature to change over from one position of equilibrium to the other. Relays of this type are known.

In this case, the switch 4 at the central station is a unipolar three-way switch to whose two outer contacts are applied the two alternating voltages, i. e. that of the power supply source and that of the amplifier 2, the voltage supplied by the direct current source 3 being applied to the middle contact of switch 4.

In the position of the relay 8 shown in the drawing the lighting means is connected to the line 1, in accord ance with the represented position of the switch 4 at the central station, hence the lighting means is connected to armature 8' of the relay 8 into its other position. Now the loudspeaker 6, instead of the lighting means 5, is connected to the line 1 and, if the switch 4 finally assumes the lefthand position, a corresponding audio-frequency voltage is applied from the amplifier 2 to said loudspeaker.

If, after the termination of the broadcast, the switch 4 is moved to its right-hand position, the direct current impulse produced on passing the middle contact causes the armature 8 of the relay 8 again to flip over, the lighting means 5 then being ready to function. In this case also, the capacitor 10 permits the alternating currents to flow substantially unimpeded past the relay winding 8 and to be supplied unweakened to the load concerned.

While the invention has been. described by means of 4 specific examples and in specific embodiments, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

7 What is claimed is:

1. A circuit-arrangement for operating a loudspeaking device with the use of a line initially present for applying a voltage from a given source to a given device, said circuitarrangement comprising a relay for selectively coupling said devices to said initially present line, an audio-frequency voltage source, a direct current source, and means for selectively connecting said sources to said line, whereby the voltage from said direct current source operates said relay to couple one of said devices to said line.

2. A circuit-arrangement as set forth in claim 1, wherein said audio-frequency source includes a low-frequency amplifier, and wherein said means for selectively connecting said sources connects said low-frequency amplifier simultaneously to its power supply after audio-frequency voltage is applied to said line.

3. A circuit-arrangement as set forth in claim 1, wherein said selective means simultaneously connects said audiofrequency voltage source and said direct current source to said line.

4. A circuit-arrangement as set forth in claim 1, wherein said relay is of a type having two stable positions and is operated by direct current impulses.

5. A circuit-arrangement as set forth in claim 4, wherein said selective means applies to said line a direct current impulse from said direct current source after disconnecting one of the other two sources from said line and prior to connecting the second of said other two sources to said line.

References Cited the file of this patent UNITED STATES PATENTS 2,002,541 Mallory et al. May 28, 1935 2,213,384 Conwell et al. Sept. 3, 1940 2,266,851 Conwell Dec. 23, 1941 

